The present invention relates to fasteners, and more particularly to a push-in fastener for retaining two parts in assembled relationship which does not require a screw thread and which assures that the fastener is centered within the aperture which it is inserted into.
Push-in fasteners are well-known and can be composed of a multiplicity of engaging projections provided around the periphery of a shank and are generally referred to as "Christmas tree fasteners". Fasteners of this type are particularly useful for retaining two panels in assembled relationship, such as a plastic interior trim anel to the body of an automobile. As is well known in the art, fastening is achieved by these "Christman Tree" fasteners since the engaging projections are designed to project radially outward from the shank a distance greater than the apertures in the parts into which they are inserted. Thus, when the shank is inserted into the apertures, the engaging projections bend toward the head of the fastener while positively engaging the inner wall of the apertures and, as each engaging projection clears the back side of the apertures, it will flex back to its original position and engage the back side of the part and prevent withdrawal of the fastener. Self centering of such a fastener is illustrated, for example, in U.S. Pat. No. 4,392,278 which discloses an "H" shaped shank cross section which contacts the inner wall of the aperture at four points. These four points correspond to the end points of each leg of the "H" and center the shank within the aperture. These fasteners however, are normally only effective for insertion into apertures over 1/8 of an inch in diameter. This is due to the fact that when the aperture size is decreased, the leg portion of the shank cross section and the engaging projections must be similarly decreased in size which makes the shank less rigid, thereby losing its centering capability. This decrease in size also affects the holding power of the engaging projections and makes the shank hard to insert since it is susceptible to bending.
The present invention overcomes the problems of previous fasteners by providing a push-in, self-centering fastener for use in any size aperture which maintains a rigid shank to enable insertion and proper holding power even when inserted into a very small aperture.